Organic Semiconductor Element

ABSTRACT

By introducing new concepts into a structure of a conventional organic semiconductor element and without using a conventional ultra thin film, an organic semiconductor element is provided which is more reliable and has higher yield. Further, efficiency is improved particularly in a photoelectronic device using an organic semiconductor. Between an anode and a cathode, there is provided an organic structure including alternately laminated organic thin film layer (functional organic thin film layer) realizing various functions by making an SCLC flow, and a conductive thin film layer (ohmic conductive thin film layer) imbued with a dark conductivity by doping it with an acceptor and a donor, or by the like method.

This application is a continuation of copending U.S. application Ser.No. 11/061,500 filed on Feb. 18, 2005 which is a continuation ofcopending U.S. application Ser. No. 10/309,843 filed on Dec. 4, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electronic device employing anorganic semiconductor. More particularly, it relates to aphotoelectronic device such as a photoelectric conversion element and anEL element.

2. Description of the Related Art

Compared to inorganic compounds, organic compounds include more variedmaterial systems, and through appropriate molecular design it ispossible to synthesize organic materials having various functionalities.Further, the organic compound is characterized in that films and thelike formed using the organic compound demonstrate great pliancy, andsuperior processability can also be achieved by polymerization. In lightof these advantages, in recent years, attention has been given tophotonics and electronics employing functional organic materials.

Photonic techniques which make use of photophysical qualities of organiccompounds have already played an important role in contemporaryindustrial techniques. For example, photosensitive materials, such as aphotoresist, have become indispensable in a photolithography technologyused for fine processing of semiconductors. In addition, since theorganic compounds themselves have properties of light absorption andconcomitant light emission (fluorescence or phosphorescence), they haveconsiderable applicability as light emitting materials such as laserpigments and the like.

On the other hand, since organic compounds do not have carriersthemselves, they essentially have superior insulation properties.Therefore, in the field of electronics where the electrical propertiesof organic materials are utilized, the main conventional use of organiccompounds is insulators, where organic compounds are used as insulatingmaterials, protective materials and covering materials.

However, there are means for making massive amounts of electricalcurrent flow in the organic materials which is essentially insulators,and they are starting to be put to practical use in the electronicsfield. The “means” discussed here can be broadly divided into twocategories.

The first of these, represented by conductive polymers, is means inwhich a π-conjugate system organic compound is doped with an acceptor(electron acceptor) or a donor (electron donor) to give the π-conjugatesystem organic compound a carrier (Reference 1: Hideki Shirakawa, EdwinJ. Louis, Alan G. MacDiarmid, Chwan K. Chiang, and Alan J. Heeger,“Synthesis of Electrically Conducting Organic Polymers HalogenDerivatives of Polyacetyrene, (CH)_(x)”, Chem. Comm., 1977, 16,578-580). By increasing the doping amount, the carrier will increase upto a certain area. Therefore, its dark conductivity will also increasetogether with this, so that significant electricity will be made toflow.

Since the amount of the electrical flow can reach the level of a normalsemiconductor or more, a group of materials which exhibit this behaviorcan be referred to as organic semiconductors (or, in some cases, organicconductors).

This means of doping the acceptor/donor to improve the dark conductivityto make the electrical current flow in the organic material is alreadybeing applied in part of the electronics field. Examples thereof includea rechargeable storage battery using polyaniline or polyacene and anelectric field condenser using polypyrrole.

The other means for making massive electrical current flow in theorganic material uses an SCLC (Space Charge Limited Current). The SCLCis an electrical current which is made to flow by injecting a spacecharge from the outside and moving it, the current density of which isexpressed by Child's Law, i.e., Formula 1, shown below. In the formula,J denotes a current density, ∈ denotes a relative dielectric constant,∈₀ denotes a vacuum dielectric constant, μ denotes a carrier mobility, Vdenotes a voltage, and d denotes a distance (hereinafter, referred to as“thickness”) between electrodes applied with the voltage V:

J=9/8·∈∈₀ μ·V ² /d ³  Formula 1

Note that the SCLC is expressed by Formula 1 in which no carrier trapwhen the SCLC flows is assumed at all. The electric current limited bythe carrier trap is referred to as a TCLC (Trap Charge Limited Current),and it is proportionate to a power of the voltage, but both the SCLC andthe TCLC are currents that are subject to bulk limitations. Therefore,both the SCLC and the TCLC are dealt with in the same way hereinbelow.

Here, for comparison, Formula 2 is shown as a formula expressing thecurrent density when an Ohm current flows according to Ohm's Law. σdenotes a conductivity, and E denotes an electric field strength:

J=σE=σ·V/d  Formula 2

In Formula 2, since the conductivity σ is expressed as σ=neμ (where ndenotes a carrier density, and e denotes an electric charge), thecarrier density is included in the factors governing the amount of theelectrical current that flows. Therefore, in an organic material havinga certain degree of carrier mobility, as long as the material's carrierdensity is not increased by doping as described above, the Ohm currentwill not flow in a material which normally does not have few carriers.

However, as is seen in Formula 1, the factors which determine the SCLCare the dielectric constant, the carrier mobility, the voltage, and thethickness. The carrier density is irrelevant. In other words, even inthe case of an organic material insulator with no carrier, by making thethickness d sufficiently small, and by selecting a material with asignificant carrier mobility μ, it becomes possible to inject a carrierfrom the outside to make the current flow.

Even when this means is used, the current flow amount can reach thelevel of a normal semiconductor or more. Thus, an organic material witha great carrier mobility μ, in other words, an organic material capableof latently transporting a carrier, can be called an “organicsemiconductor”.

Incidentally, even among organic semiconductor elements which use theSCLC as described above, organic electroluminescent elements(hereinafter, referred to as “organic EL elements”) which use both thephotonic and electrical qualities of functional organic material asphotoelectronic devices, have particularly demonstrated remarkableadvancement in recent years.

The most basic structure of the organic EL element was reported by W.Tang, et al. in 1987 (Reference 2: C. W. Tang and S. A. Vanslyke,“Organic electroluminescent diodes”, Applied Physics Letters, Vol. 51,No. 12, 913-915 (1987)). The element reported in Reference 2 is a typeof diode element in which electrodes sandwich an organic thin filmhaving a total thickness of approximately 100 nm and being constitutedby laminating a hole-transporting organic compound and anelectron-transporting organic compound, and the element uses a lightemitting material (fluorescent material) as the electron-transportingcompound. By applying voltage to the element, light-emission can beachieved as from a light emitting diode.

The light-emission mechanism is considered to work as follows. That is,by applying the voltage to the organic thin film sandwiched by theelectrodes, the hole and the electron injected from the electrodes arerecombined inside the organic thin film to form an excited molecule(hereinafter, referred to as a “molecular exciton”), and light isemitted when this molecular exciton returns to its base state.

Note that, types of molecular excitons formed by the organic compoundcan include a singlet excited state and a triplet excited state, and thebase state is normally the singlet state. Therefore, emitted light fromthe singlet excited state is referred to as fluorescent light, and theemitted light from the triplet excited state is referred to asphosphorescent light. The discussion in this specification covers casesof contribution to the emitted light from both of the excited states.

In the case of the organic EL element described above, the organic thinfilm is normally formed as a thin film having a thickness of about 100to 200 nm. Further, since the organic EL element is a self-luminouselement in which light is emitted from the organic thin film itself,there is no need for such a back light as used in a conventional liquidcrystal display. Therefore, the organic EL element has a great advantagein that it can be manufactured to be extremely thin and lightweight.

Further, in the thin film having a thickness of about 100 to 200 nm, forexample, the time from when the carrier is injected to when therecombination occurs is approximately several tens of nanoseconds, giventhe carrier mobility exhibited by the organic thin film. Even when thetime required by for the process form the recombination of the carrierto the emission of the light, it is less than an order of microsecondsbefore the light emission. Therefore, one characteristic of the organicthin film is that response time thereof is extremely fast.

Because of the above-mentioned properties of thinness andlightweightness, the quick response time, and the like, the organic ELelement is receiving attention as a next generation flat panel displayelement. Further, since it is self-luminous and its visible range isbroad, its visibility is relatively good and it is considered effectiveas an element used in display screens of portable devices.

Further, in addition to the organic EL element, an organic solar batteryis another representative example of an organic semiconductor elementusing organic material (i.e., an organic semiconductor) capable oftransporting carriers latently, which is to say having a certain degreeof carrier mobility.

In short, the organic solar battery utilizes an opposite structure tothe organic EL element. That is, its structure is similar to the mostbasic structure of the organic EL element, where the organic thin filmhaving the two-layer structure is sandwiched by electrodes (Reference 3:C. W. Tang, “Two-layer organic photovoltaic cell”, Applied PhysicsLetters, vol. 48, No. 2, 183-185 (1986)). A photoelectric currentgenerated by causing light to be absorbed into the organic thin film isused to obtain an electromotive force. The electric current that flowsat this time can be understood as follows: the carrier generated by thelight flows due to the carrier mobility present in the organic material.

In this way, the organic material, which was considered as having nopurpose in the electronics field other than its original purpose as aninsulator, can be made to perform central functionalities in variouselectronic devices and photoelectronic devices by skillfully devisingthe organic semiconductor. Accordingly, research in organicsemiconductors has become robust at present.

Description has been made above regarding two methods using the organicsemiconductor as means for flowing the electric current to the organicmaterial which is essentially an insulator. However, each of these twomethods has a different problem.

First, in the case where the acceptor and the donor are doped to theorganic semiconductor to increase the carrier densities, theconductivity is actually improved but the organic semiconductor itselfloses its own physical properties (light absorption, phosphorescence,etc.) which it originally had. For example, when a phosphorescent-lightemitting π-conjugate system polymer material is doped with theacceptor/donor, its conductivity increases but it stops emitting light.Therefore, in exchange for obtaining the functionality of conductivity,the other various functionalities which the organic material possessesare sacrificed.

Further, although there is an advantage in that various conductivitiescan be achieved by adjusting a doping amount of the acceptor or thedonor, no matter how much acceptor and donor are doped to increase thecarrier, it is difficult to constantly obtain a carrier densityequivalent to a metal or of an inorganic compound that is equivalent toa metal (e.g., nitride titan or other such inorganic compoundconductor). In other words, with respect to conductivity, it isextremely difficult to surpass an inorganic material, except for inseveral examples. Thus, the only remaining advantage is that the organicmaterial is extremely workable and pliant.

On the other hand, in the case where the SCLC (hereinafter, SCLCincludes a photoelectric current) is made to flow to the organicsemiconductor, the physical properties that the organic semiconductororiginally had are not lost. A representative example of such is noneother than the organic EL element, in which the light emission from thefluorescent material (or phosphorescent material) is utilized even whenthe electric current is made to flow. The organic solar battery alsoutilizes the functionality of light absorption by the organicsemiconductor.

However, as can be understood by looking at Formula 1, since the SCLC isinversely proportionate to the 3rd power of the thickness d, the SCLCcan only be made to flow through a structure consisting of electrodessandwiched to both surfaces of extremely thin films. More specifically,in light of the general carrier mobility of organic materials, thestructure must be an ultra thin film of approximately 100 nm to 200 nm.

It is true, however, that by adopting the above-mentioned ultra thinfilm structure, a significant amount of SCLC can be made to flow at lowvoltage. One reason why the organic EL element such as the one discussedin Reference 2 is successful is because the thickness of its organicthin film is designed as a uniformly ultra thin film having a thicknessof approximately 100 nm.

However, the fact that the thickness d must be made extremely thinactually becomes the biggest problem when the SCLC is made to flow.First, in the 100 nm thin film, it is easy for pinholes and other suchdefects to develop, and short circuits and other such problems occur dueto these, causing a concern that yield may deteriorate. Further, notonly does the mechanical strength of the thin film decline, but also themanufacturing process itself is restricted because the film must be anultra thin film.

Further, when the SCLC is used as the electric current, the physicalproperties that the organic semiconductor itself originally possessedare not lost, and there is an advantage in that various functionalitiescan be produced. However, deterioration of the functionality of theorganic semiconductor is accelerated by making the SCLC flow. Forexample, looking at the organic EL element as an example, it is knownthat the lifetime of the element (i.e., the half-life of the brightnesslevel of the emitted light) deteriorates almost in inverse proportion toits original brightness, or, in other words, to the amount of electricalcurrent that is made to flow (Reference 4: Yoshiharu SATO, “The JapanSociety of Applied Physics/Organic Molecular Electronics andBioelectronics”, vol. 11, No. 1 (2000), 86-99).

As described above, in the device where the acceptor or the donor isdoped to produce conductivity, functionalities other than theconductivity are lost. Further, in the device where the SCLC is used toproduce the conductivity, the flowing of massive amounts of anelectrical current through the ultra thin film becomes a cause ofproblems regarding the element's reliability and the like.

Incidentally, in photoelectronic devices using the organicsemiconductors, such as organic EL elements and organic solar batteries,there is also a problem with respect to efficiency.

The organic EL element will be discussed as an example. The lightemitting mechanism of the organic EL element is that the injected holeand electron recombine with each other to be converted into light.Therefore, theoretically, it is possible to extract at most one photonfrom the recombination of one hole and one electron, and it is not bepossible to extract a plurality of photons. That is, the internalquantum efficiency (the number of emitted photons with respect injectedcarriers) should be at most 1.

However, in reality, it is difficult to bring the internal quantumefficiency close to 1. For example, in the case of the organic ELelement using the fluorescent material as the light emitting body, thestatistical ratio of generation for the singlet excited state (S*) andthe triplet excited state (T*) is considered to be S*:T*=1:3 (Reference5: Tetsuo TSUTSUI, “Textbook of the 3rd seminar at Division of OrganicMolecular Electronics and Bioelectronics, The Japan Society of AppliedPhysics”, p. 31 (1993)). Therefore, the theoretical limit of theinternal quantum efficiency is 0.25. Furthermore, as long as thefluorescent quantum yield from the fluorescent material is not φ_(f),the internal quantum efficiency will drop even lower than 0.25.

In recent years, attempts have been made to use phosphorescent materialsto use the light emission from the triplet excited state to bring theinternal quantum efficiency's theoretical limit close to 0.75 to 1, andthe efficiency actually surpassing that of fluorescent material has beenachieved. However, in order to achieve this, it is necessary to use aphosphorescent material with a high phosphorescent quantum efficiencyφ_(p). Therefore, the range of selection for the material is unavoidablyrestricted. This is because organic compounds that can emitphosphorescent light at room temperature are extremely rare.

In other words, if means could be structured for improving theelectrical current efficiency (the brightness level generated inrelation to the electrical current) of the organic EL element, thiswould be a great innovation. If the electrical current efficiency isimproved, a greater level of brightness can be produced with a smallerelectrical current. Conversely, since the electrical current can bereduced for achieving a certain brightness level, the deteriorationcaused by the massive amount of electrical current made to flow to theultra thin film as described above can be reduced.

The inverse structure of the organic EL element, which is to say thephotoelectric conversion such as in the organic solar battery, isinefficient at present. As described above, in the organic solar batteryusing the conventional organic semiconductor, the electrical currentdoes not flow if the ultra thin film is not used. Therefore,electromotive force is not produced, either. However, when the ultrathin film is adopted, a problem arises in that the light absorptionefficiency is poor (i.e., the light cannot be completely absorbed). Thisproblem is considered to be the largest reason for the poor efficiency.

In light of the foregoing discussion, the electronic device using theorganic semiconductor has a shortcoming in that when the massiveelectrical current is made to flow in a device utilizing the physicalproperties that are unique to the organic material, the reliability andyield from the device is influenced unfavorably. Furthermore,particularly in the photoelectronic device, the efficiency of the deviceis poor. These problems basically can be said to arise from the “ultrathin film” structure of the conventional organic semiconductor element.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to introduce a newconcept to the structure of the conventional organic semiconductorelement, to provide an organic semiconductor element with not onlygreater reliability but also higher yield, without using theconventional ultra thin film. Another object of the present invention isto improve the efficiency of the photoelectronic device using theorganic semiconductor.

The inventor of the present invention, as a result of repeated intensestudies, has devised means capable of achieving the above-mentionedobject by combining an organic semiconductor that is doped with anacceptor or a donor to make it conductive, and an organic semiconductorin which an SCLC is used to achieve the conductivity. The most basicstructure thereof is shown in FIG. 1.

FIG. 1 shows an organic semiconductor element comprised of an organicstructure in which, between an anode and a cathode, there arealternatively laminated an organic thin film layer (referred to as a“functional organic thin film layer” in the present specification) forrealizing various functionalities by flowing an SCLC, and a conductivethin film layer in a floating state in which a dark conductivity isachieved by doping the acceptor or donor, or by another method.

What is important here, is that the conductive thin film layer should beconnected substantially ohmically to the functional organic thin filmlayer (in this case, the conductive thin film layer is particularlyreferred to as an “ohmic conductive thin film layer”). In other words,obstructions between the conductive thin film layer and the functionalorganic thin film layer should be eliminated or extremely minimized.

By adopting the above structure, holes and electrons are easily injectedeach from the ohmic conductive thin film layers into each of thefunctional organic thin film layers. For example, a conceptual diagramof an element shown in FIG. 1 as n=2 is shown in FIGS. 2A and 2B. InFIGS. 2A and 2B, when an electrical voltage is applied between the anodeand the cathode, electrons are easily injected from a first ohmicconductive thin film layer into a first functional organic thin filmlayer, and the holes are easily injected from the first ohmic conductivethin film layer into a second functional organic thin film layer. Whenviewed from an external circuit, a hole moves from the anode toward thecathode, and an electron moves from the cathode toward the anode (FIG.2A). However, it can also be understood that both the electron and thehole flow from the ohmic conductive thin film layer back toward theopposite directions (FIG. 2B).

Here, by making each functional organic thin film layer to have athickness of 100 nm to 200 nm or smaller, the carrier injected into eachfunctional organic thin film layer can be made to flow as the SCLC. Thatis, in each functional organic thin film layer, a functionality (such aslight emission or the like) derived from the inherent physicality of theorganic material can be realized.

Moreover, when the basic structure of the present invention is applied,the organic structure can be made to have any degree of thickness, whichis extremely useful. In other words, assume that in the conventionalelement (in which a functional organic thin film layer 303 is sandwichedbetween a cathode 301 and a anode 302), a given electrical voltage V isapplied to the film thickness d to thereby obtain an electrical currentdensity of J (FIG. 3A). Here, in the case of the present invention (FIG.3B) with the alternatively laminated n number of functional organic thinfilm layers 303 similarly having film thickness d and (n−1) number ofohmic conductive thin film layers 304, where it was only possible toflow the SCLC into the thickness d (which was 100 nm to 200 nm in theconventional art), the present invention appears equivalent to flowingan SCLC having the current density J to a film thickness nd, just as inthe case shown in FIG. 3A. In other words, the effect is that of FIG.3C, but this is impossible in the conventional art because no matter howmuch voltage is applied, the SCLC suddenly stops flowing if the filmthickness becomes very thick.

Of course, this simply means only that an electrical voltage nV isrequired. However, the electronic devices using the organicsemiconductor can easily overcome the problem in that by utilizing theorganic material's inherent physical properties, when a massive amountof electrical current is made to flow, there is a negative effect on thereliability and the yield of the device.

Thus, by providing the organic structure with the alternately laminatedfunctional organic thin film layer and conductive thin film layer, theorganic semiconductor element can make the SCLC flow in greater filmthickness than in the conventional art. This concept did not exist untilnow. This concept can obviously be applied in organic EL elements wherethe SCLC is made to flow to achieve light emission and in organic solarbatteries which utilize a photoelectric current and are said to have theopposite mechanism of the organic EL elements. The concept can also beapplied broadly to other organic semiconductor elements.

Therefore, according to the present invention, there is provided anorganic semiconductor element comprised of an organic structure formedby sequentially laminating an n number of functional organic thin filmlayers (where n is an integer equal to or greater than 2) consisting ofa first through an n-th functional organic thin film layers between ananode and a cathode, characterized in that: a conductive thin film layerin a floating state is without exception formed between a k-thfunctional organic thin film layer (where k is an integer of 1≦k≦(n−1))and a (k+1)th functional organic thin film layer; and each of theconductive thin film layers ohmically contacts with each of thefunctional organic thin film layer.

In this case, as the conductive thin film layer, it is preferable to usean organic compound instead of using a metal or a conductive inorganiccompound. Particularly in the case of the photoelectronic device whichrequires transparency, it is preferable to use the organic compound.

Therefore, according to the present invention, there is provided anorganic semiconductor element comprised of an organic structure formedby sequentially laminating an n number of functional organic thin filmlayers (where n is an integer equal to or greater than 2) consisting ofa first through an n-th functional organic thin film layers between ananode and a cathode, characterized in that: a conductive thin film layerin a floating state which includes an organic compound is withoutexception fondled between a k-th functional organic thin film layer(where k is an integer of 1≦k≦(n−1)) and a (k+1)th functional organicthin film layer; and each of the conductive thin film layers ohmicallycontacts with each of the functional organic thin film layer.

Also, in order to contact the conductive thin film layer with thefunctional organic thin film layer ohmically or in a substantiallyequivalent manner, as described above, it is important to adopt themeans in which the conductive thin film layer is formed of the organiccompound and the layer is doped with the acceptor or the donor.

Therefore, according to the present invention, there is provided anorganic semiconductor element comprised of an organic structure formedby sequentially laminating an n number of functional organic thin filmlayers (where n is an integer equal to or greater than 2) consisting ofa first through an n-th functional organic thin film layers between ananode and a cathode, characterized in that: a conductive thin film layerin a floating state which includes an organic compound is withoutexception formed between a k-th functional organic thin film layer(where k is an integer of 1≦k≦(n−1)) and a (k+1)th functional organicthin film layer; and each of the conductive thin film layers contains atleast one of an acceptor and a donor for the organic compound.

Also, according to the present invention, there is provided an organicsemiconductor element comprised of an organic structure formed bysequentially laminating an n number of functional organic thin filmlayers (where n is an integer equal to or greater than 2) consisting ofa first through an n-th functional organic thin film layers between ananode and a cathode, characterized in that: a conductive thin film layerin a floating state which includes an organic compound is withoutexception formed between a k-th functional organic thin film layer(where k is an integer of 1≦k≦(n−1)) and a (k+1)th functional organicthin film layer; and each of the conductive thin film layers containsboth of an acceptor and a donor for the organic compound.

Note that, when the conductive thin film layer is doped with theacceptor or the donor, the organic compound used in the functionalorganic thin film layer and the organic compound used in the conductivethin film layer are connected with the same thing (i.e., the organiccompound used in the functional organic thin film layer is included intothe conductive thin film layer, and the conductive thin film layer isdoped with the acceptor or the donor). This enables the element to bemanufactured according to a simple process.

Incidentally, in the case where both the acceptor and the donor areincluded in the conductive thin film layer, it is preferable that: theconductive thin film layer be structured by laminating a first layerformed by adding an acceptor to the organic compound, and a second layerformed by adding a donor to an organic compound that is the same as theorganic compound; and the first layer be positioned closer to a cathodeside than the second layer.

Also, in such a case, it is preferable that the organic compound used inthe functional organic thin film layer and the organic compound used inthe conductive thin film layer be connected with the same thing.

Incidentally, in the case where both the acceptor and the donor areincluded in the conductive thin film layer, it is also preferable that:the conductive thin film layer be structured by laminating a first layerformed by adding an acceptor to a first organic compound, and a secondlayer formed by adding a donor to a second organic compound that isdifferent from the first organic compound; and the first layer bepositioned closer to a cathode side than the second layer.

Also, in such a case, it is preferable that the organic compound used inthe functional organic thin film layer and the organic compound used inthe first layer be connected with the same thing. Also, it is preferablethat the organic compound used in the functional organic thin film layerand the organic compound used in the second layer be connected with thesame thing.

The structure of the functional organic thin film layer may bemanufactured using a bipolar organic compound, or by combining monopolarorganic compounds by laminating a hole transporting layer and anelectron transporting layer, for example.

The element structure described above is extremely useful among organicsemiconductor elements particularly because in the photoelectronicsfield it can increase light emission efficiency and light absorptionefficiency. That is, by structuring the functional organic thin filmlayer with the organic compound that exhibits light emission by flowingthe electrical current, the organic EL element with high reliability andgood efficiency can be created. Further, by structuring the functionalorganic thin film layer with the organic compound which generates thephotoelectric current (i.e., generates the electromotive force) byabsorbing light, the organic solar battery with high reliability andgood efficiency can be created.

Therefore, the present invention includes everything related to theorganic semiconductor element in which the functional organic thin filmlayer described above has the structure capable of realizing the organicEL element functionality and the organic solar battery functionality.

Note that, particularly in the organic EL element, in the case where thefunctional organic thin film layer is structured with the bipolarorganic compound, the bipolar organic compound preferably includes ahigh molecular compound having a π-conjugate system. Further, for theconductive thin film layer as well, it is desirable to use a method inwhich the high molecular compound having an π-conjugate system is usedand the layer is doped with the acceptor or the donor to improve thedark conductivity. Alternatively, for the conductive thin film layer, itis also possible to use a conductive high molecular compound with theacceptor or donor added thereto.

Further, in the organic EL element, in the case where, for example, thehole transporting layer made of a hole transporting material, and theelectron transporting layer made of an electron transporting material,are laminated to structure the functional organic thin film layer bycombining monopolar organic compounds, the conductive thin film layershould also be made using at least one of the hole transporting materialand the electron transporting material, and the layers should be dopedwith the acceptor and donor to increase the dark conductivity.

Alternatively, it is also possible to use both the hole transportingmaterial and the electron transporting material. In more specific terms,this refers to a method in which a donor-doped layer of the electrontransporting material used in the functional organic thin film layer,and an acceptor-doped layer of the hole transporting material used inthe functional organic thin film layer, are laminated upon each other ina structure used as the conductive thin film layer.

The structure of the functional organic thin film layer when used in theorganic solar battery is the same as when used in the organic ELelement. That is, in the organic solar battery, in the case where thefunctional organic thin film layer is structured with the bipolarorganic compound, the bipolar organic compound preferably includes ahigh molecular compound having the π-conjugate system. Further, for theconductive thin film layer as well, it is desirable to use a method inwhich the high molecular compound having the π-conjugate system is usedand the layer is doped with the acceptor or the donor to improve thedark conductivity. Alternatively, for the conductive thin film layer, itis also possible to use the conductive high molecular compound with theacceptor or donor added thereto.

Further, in the organic solar battery, in the case where, for example,the layer made of the hole transporting material, and the layer made ofthe electron transporting material, are laminated to structure thefunctional organic thin film layer by combining monopolar organiccompounds, the conductive thin film layer should also be made using atleast one of the hole transporting material and the electrontransporting material, and the layers should be doped with the acceptorand donor to increase the dark conductivity. Alternatively, it is alsopossible to use both the hole transporting material and the electrontransporting material. In more specific terms, this refers to a methodin which the donor-doped layer of the electron transporting materialused in the functional organic thin film layer, and the acceptor-dopedlayer of the hole transporting material used in the functional organicthin film layer are laminated upon each other in the structure used asthe conductive thin film layer.

Note that, if the carrier can be injected into all the conductive thinfilm layers (ohmic conductive thin film layers) described above, then itis not necessary to reduce sheet resistance in any of them. Accordingly,a conductivity rate of 10⁻¹⁰ S/m or greater is sufficient.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 shows a basic structure of the present invention;

FIGS. 2A and 2B show concepts of the present invention;

FIGS. 3A to 3C show effects produced by the present invention;

FIGS. 4A and 4B illustrate theory behind improvement in electricalcurrent efficiency;

FIG. 5 shows theory behind improvement in the electrical currentefficiency;

FIGS. 6A and 6B depict conventional organic EL elements;

FIG. 7 shows an organic EL element according to the present invention;

FIG. 8 shows a specific example of an organic EL element according tothe present invention;

FIG. 9 shows a specific example of an organic EL element according tothe present invention; and

FIG. 10 shows a specific example of an organic EL element according tothe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, detailed explanation is made with respect to embodiments ofthe present invention, using an organic EL element and an organic solarbattery as examples. Note that, with respect to the organic EL element,in order to achieve light emission, it is sufficient if at least one ofan anode and a cathode is made transparent. However, in accordance withthis embodiment mode, description is made of an element structure inwhich a transparent anode is formed on a substrate to achieve the lightfrom the anode side. In actuality, the present invention may be appliedin a structure in which the cathode is formed onto the substrate toachieve the light from the cathode side, and in a structure in which thelight is achieved from an opposite side from the substrate, and in astructure in which the light is achieved from both the electrodes onboth sides. In the organic solar battery as well, in order to make thebattery absorb light, any one side of the element may be madetransparent.

First, in the organic EL element, as means for overcoming the poorreliability deriving from the ultra thin film and also for improving theproportion of light emitted in relation to the electrical current (i.e.,the electrical current efficiency), in order to achieve a simple devicestructure, the organic EL element may be connected serially, forexample. This will be explained below.

As shown in, FIG. 4A, assume an organic EL element D₁, in which applyinga certain electrical voltage V₁ causes an electric current with anelectric density J₁ to flow and light is emitted by a light energy perunit surface area L₁ (i.e., photons having certain amounts of energy areemitted, and the light energy is equivalent to the product of thatenergy multiplied by the number of photons). At this time, a powerefficiency φe₁ (this refers to the light emission energy with respect tothe electrical energy (electrical power) that was given, and it meansthe same thing as an “energy conversion rate”) is given in the followingformula:

φe ₁ =L ₁/(J ₁ ·V ₁)  Formula 3

Next, a case will be considered in which an organic EL element D₂ thatis exactly equivalent to the organic EL element D₁ is connected to theorganic EL element D₁ serially (See FIG. 4B). Note that, a contact pointC₁ connects the two elements D₁ and D₂ together ohmically.

Here, the elements as a whole (i.e., element D_(all) having thestructure consisting of D₁ and D₂ connected to each other) are appliedwith a voltage V₂ (=2V₁) that is double the voltage that was applied inFIG. 4A. Then, since D₁ and D₂ are equivalent to each other, the voltageV₁ is applied to D₁ and to D₂, respectively, as shown in FIG. 4B, andthe shared electrical current density J₁ flows. Therefore, since D₁ andD₂ each emit light with the light energy L₁, double the light energy 2L₁can be obtained from the elements as a whole D_(all).

The power efficiency φe₂ at this time is given in the following formula:

φe ₂=2L ₁/(J ₁·2V ₁)=L ₁/(J·V ₁)  Formula 4

As can be understood by comparing the above-mentioned Formula 3 and theabove-mentioned Formula 4, there is no difference between FIG. 4A andFIG. 4B in terms of the power efficiency, and the law of energyconservation in which V₁ and J₁ are converted to L₁ is being obeyed.However, the current efficiency appears to increase twofold, i.e., L₁/J₁is increased to 2L₁/J₁. This has a significant meaning for the organicEL element. That is, by increasing the organic EL elements connectedserially and by applying more voltage in proportion to the number ofelements that were increased and maintaining the current density at afixed level, it becomes possible to increase the electrical currentefficiency.

Examining this concept more generally, when n number of the entirelyequivalent organic EL elements are ohmically connected, it is possibleto achieve n times the brightness level by maintaining the currentdensity at a fixed level and increasing the electrical voltage by ntimes. This property derives from the proportional relationship betweenthe brightness level and the electrical current density level in theorganic EL element.

Of course, even in the case where different organic EL elements areconnected serially, the brightness level emitted from each of theorganic EL elements will be different. However, by significantlyincreasing the voltage, it becomes possible to extract more brightnessthan in the case of a single organic EL element. A conceptual diagram ofthis is shown in FIG. 5.

As shown in FIG. 5, when the different organic EL elements D₁ and D₂ areconnected serially and one of the organic EL elements (either D₁ or D₂)is applied with a higher voltage V₁+V₂ than the necessary voltage(either V₁ or V₂) to create the electrical current J₁, a brightnesslevel L₁+L₂ (>L₁, L₂) can be produced with the current J₁.

At this time, by configuring, for example, D₁ as a blue light emittingelement and D₂ as a yellow light emitting element, if color mixing canbe performed, then a white color light emission will occur. Therefore,this enables a white color emitting element in which the electricalcurrent efficiency is higher, and therefore the longevity of the elementis higher than in the conventional art.

As described above, by ohmically connecting the elements serially, theapparent electrical current efficiency is improved and greaterbrightness can be obtained with a smaller electrical current. This meansthat it is possible to make the necessary electrical current foremission of the same level of brightness is kept smaller than in theconventional art. Furthermore, as long as a significant electricalvoltage can be applied, it is possible to connect however many organicEL elements as may be needed, and the overall film thickness can be madethick.

However, as described above, a problem occurs even in the case where theorganic EL elements are simply connected serially. The problem derivesfrom the electrodes for the organic EL elements and from the elementstructure, which will be explained using FIG. 6. FIG. 6A shows across-sectional view of the organic EL element D₁ shown in FIG. 4A, andFIG. 6B shows a cross sectional view of all the elements D_(all) shownin FIG. 4B, in a schematic manner.

The basic structure (FIG. 6A) of the normal organic EL element ismanufactured by providing a transparent electrode 602 onto a substrate601 (here, the electrode is an anode, and an ITO or the like isgenerally used for this), a functional organic thin film layer(hereinafter, referred to as an “organic EL layer”) 604 for performinglight emission by flowing an electrical current is then formed and acathode 603 is then provided. With this structure, light can be producedfrom the transparent electrode (the anode) 602. The cathode 603 may be acathode which normally employs both a metallic electrode with a low workfunction, or an electron injecting cathode buffer layer, along with ametallic conductive film (such as aluminum or the like).

When two organic EL elements having the structure described above areconnected simply serially (as shown in FIG. 6B), the structure willinclude a first transparent electrode (cathode) 602 a, a first organicEL layer 604 a, a first cathode 603 a, a second organic EL layer 604 b,a second organic EL layer 604 b, and a second cathode 603 b, which arelaminated in this order from the lower side. Then, the light emitted bythe second organic EL layer 604 b cannot be transmitted through becausethe first cathode 603 a which is metal, and thus the light cannot betaken out of the element. Therefore, it becomes impossible to do suchinnovations as mixing the light emission from the upper and the lowerorganic EL elements to produce the white color light.

For example, a technique using transparent ITO cathodes for both theanode and the cathode has also be reported (Reference 6: G.Parthasarathy, P. E. Burrows, V. Khalfin, V. G. Kozlov, and S. R.Forrest, “A metal-free cathode for organic semiconductor devices”, J.Appl. Phys., 72, 2138-2140 (1998)). By using this, the first cathode 603a can be made transparent. Therefore, it becomes possible to bring outthe light emitted from the second organic EL layer 604 b. However, sincethe ITOs are mainly formed by sputtering, there is a concern that theorganic EL layer 604 a will suffer damage. Further, the process alsobecomes cumbersome because the application of the organic EL layer bydeposition and the application of the ITO by sputtering have to berepeated.

In order to overcome this problem, a more desirable embodiment has astructure such as shown in FIG. 7, for example, in which the electricalcurrent efficiency can be improved using a concept similar connectingthe elements serially to improve the electrical current efficiency, andalso the element transparency issue can be cleared without a problem.

FIG. 7 shows a structure in which a first organic EL layer 704 a, afirst conductive thin film layer 705 a, a second organic EL layer 704 b,and a cathode 703 are laminated in this order on a transparent electrode(anode) 702 that is provided to a substrate 701. In this structure, byapplying a material in which the acceptor or the donor has been appliedto the organic semiconductor, the first semiconductor thin film layer705 a can be connected almost ohmically to the organic EL layer (i.e.,the hole carrier and the electron carriers can be injected), and,moreover, the transparency can be maintained almost completely.Therefore, the light emission that is generated with the second organicEL layer 703 b can be brought out, and the electrical current efficiencycan be doubled simply by doubling the electrical voltage.

Moreover, since the entire process becomes consistent (for example, whenusing low molecular materials, a dry process such as vacuum depositioncan be used, and when using high molecular materials, a wet process suchas spin coating can be used), the manufacturing process does not becomecumbersome.

Note that, FIG. 7 shows the structure in which two of organic EL layershave been provided. However, as described above, as long as asignificant amount of electrical voltage may be applied, the structuremay be multi-layered (of course, the conductive thin film layer isinserted between each of the organic EL layers). Therefore, the poorreliability of the organic semiconductor element, which is derived fromthe ultra thin film structure, can be overcome.

The philosophy described above naturally can also be applied in theorganic solar battery, which is said to utilize the opposite mechanismfrom the organic EL element. This will explained as follows.

It is assumed here that there is an organic solar battery S₁ in which agiven light energy L₁ generates a photoelectric current with anelectrical current density J₁, thus generating an electromotive forceV₁. N number of the batteries S₁ are ohmically connected serially, andwhen a light energy nL₁ is irradiated there, n times the electromotiveforce (=nV₁) can be obtained if an equivalent light energy nL₁/n=L₁) canbe provided to all the n number of solar batteries S₁. In short, if allthe organic solar batteries that are connected serially can absorb thelight, then the electromotive force increases as a product of the numberof batteries.

For example, there is a report that discloses improving theelectromotive force by connecting two organic solar batteries serially(Reference 7: Masahiro HIRAMOTO, Minoru SUEZAKI, and Masaaki YOKOYAMA,“Effect of Thin Gold Interstitial-layer on the Photovoltaic Propertiesof Tandem Organic Solar Cell”, Chemistry Letters, pp. 327-330, 1990).According to Reference 7, by inserting a gold thin film between the twoorganic solar batteries (i.e., between a front cell and a back cell) aneffect of improving the electromotive force generated by the lightirradiation is obtained.

However, Reference 7 also structures the gold thin film to have athickness of 3 nm or less in order to achieve the transmittivity. Inother words, the film is structured as an ultra thin film that is thinenough for light to pass through it, designed so that the light willreach the back cell. Moreover, reproducibility becomes problematic whenthe thickness of the ultra thin film is on the order of several nm.

Such problems can also be resolved by using the present invention. Thatis, in the organic solar battery structure such as disclosed inReference 7, the present invention may be applied at the gold thin filmportion. By doing this, the present invention can be used as a singleorganic solar battery that is thicker and more highly efficient than theconventional art, instead of connecting two elements serially.

The basic concepts and structures of the present invention have beendescribed above using the organic EL element and the organic solarbattery as examples. The following describes preferred examples ofstructures of the conductive thin film layer to be used for the presentinvention. However, the present invention is not limited to theseexamples.

First, various metallic thin films can, be used because they areconductive, which is to say they have multiple carriers. Specifically,Au, Al, Pt, Cu, Ni, etc. are examples that can be used. Note that, whenthese metals are used for the conductive thin film layer, it ispreferable that they be formed as ultra thin films thin enough forvisible light to pass through (i.e., several nm to several tens of nm).

Further, various metallic oxide thin films can be used, particularlyfrom the viewpoint of visible light transmittivity. Specific examplesinclude ITO, ZnO, SnO₂, copper oxide, cobalt oxide, zirconium oxide,titanium oxide, niobium oxide, nickel oxide, neodymium oxide, vanadiumoxide, bismuth oxide, beryllium aluminum oxide, boron oxide, magnesiumoxide, molybdenum oxide, lanthanum oxide, lithium oxide, ruthenium oxideand BeO. Further, compound semiconductor thin films can also be used,including ZnS, ZnSe, GaN, AlGaN, and CdS.

A particular characteristic of the present invention is that theconductive thin film layer can be structured of an organic compound. Forexample, there is a technique for mixing a p-type organic semiconductorand an n-type organic semiconductor to form the semiconductor thin filmlayer.

Typical examples of a p-type organic semiconductor include, in additionto CuPc represented by Chem. 1 below, phthalocyanine bound to the othermetals or bound to no metals (represented by Chem. 2 below). Thefollowing can be also used as the p-type organic semiconductor: TTF(represented by Chem. 3 below); TTT (represented by Chem. 4 below);methylphenothiazine (represented by Chem. 5 below); N-isopropylcarbazole(represented by Chem. 6 below); and the like. Further, a holetransporting material used for organic EL etc., such as TPD (representedby Chem. 7 below), α-NPD (represented by Chem. 8 below), or CBP(represented by Chem. 9 below) may be also applied thereto.

Typical examples of an n-type organic semiconductor include, in additionto F₁₆-CuPc represented by Chem. 10 below, 3,4,9,10-perylenetetracarboxylic acid derivatives such as PV (represented by Chem. 11below), Me-PTC (represented by Chem. 12 below), or PTCDA (represented byChem. 13 below), naphthalenecarboxylic anhydrides (represented by Chem.14 below), naphthalenecarboxylic diimide (represented by Chem. 15below), or the like. The following can be also used as the n-typeorganic semiconductor: TCNQ (represented by Chem. 16 below); TCE(represented by Chem. 17 below); benzoquinone (represented by Chem. 18below); 2,6-naphthoquinone (represented by Chem. 19 below); DDQ(represented by Chem. 20 below), p-fluoranil (represented by Chem. 21below); tetrachlorodiphenoquinone (represented by Chem. 22 below);nickelbisdiphenylglyoxime (represented by Chem. 23 below); and the like.Further, an electron transporting material used for the organic EL etc.,such as Alq₃ (represented by Chem. 24 below), BCP (represented by Chem.25 below), or PBD (represented by Chem. 26 below) may be also appliedthereto.

Further, in another preferred technique, an organic compound acceptor(electron acceptor) and an organic compound donor (electron donor) aremixed and a charge-transfer complex is formed to make the conductivethin film layer to create conductivity to serve as the conductive thinfilm layer. The charge-transfer complex crystallizes easily and is noteasy to apply as a film. However, the conductive thin film layeraccording to the present invention may be formed as a thin layer or in acluster-shape (as long as the carriers can be injected). Therefore, nosignificant problems occur.

Representative examples of combinations for the charge-transfer complexinclude the TTF-TCNQ combination shown in Chem. 27 shown below, andmetal/organic acceptors such as K-TCNQ and Cu-TCNQ. Other combinationsinclude [BEDT-TTF]-TCNQ (Chem. 28 below), (Me)₂P—C₁₈TCNQ (Chem. 29below), BIPA-TCNQ (Chem. 30 below), and Q-TCNQ (Chem. 31 below). Notethat, these charge-transfer complex thin films can be applied either asdeposited films, spin-coated films, LB film, polymer binder dispersedfilms, or the like.

Further, as a structural example of a conductive thin-film layer, atechnique of doping an acceptor or a donor into an organic semiconductorto apply a dark conductivity thereto is preferably used. An organiccompound having a π-conjugate system represented by a conductive polymeretc. may be used for the organic semiconductor. Examples of theconductive polymer include materials put into practical use, such aspoly(ethylenedioxythiophene) (abbreviated to PEDOT), polyaniline, orpolypyrrole, and in addition thereto, polyphenylene derivatives,polythiophene derivatives, and poly(paraphenylene vinylene) derivatives.

Also, when the acceptor is doped, it is preferable that a p-typematerial be used for the organic semiconductor. Examples of the p-typeorganic semiconductor may include those represented by Chems. 1 to 9 asdescribed above. At this time, Lewis acid (strongly acidic dopant) suchas FeCl₃ (III), AlCl₃, AlBr₃, AsF₆, or a halogen compound may be used asthe acceptor (Lewis acid can function as the acceptor).

Further, in the case where the donor is doped, it is preferable to usean n-type material for the organic semiconductor. Examples of n-typeorganic semiconductors include the above-mentioned Chems. 10 to 26 andthe like. Then, for the donor, alkali metals such as represented by Li,K, Ca, Cs and the like, or a Lewis base such as an alkali earth metal(the Lewis base can function as the donor) may be used.

More preferably, several of the structures described above can becombined to serve as the conductive thin film layer. In other words, forexample, on one side or both sides of an inorganic thin film such as theabove-mentioned metallic thin film, metallic oxide thin film, orcompound semiconductor thin film can be formed with a thin film in whicha p-type organic semiconductor is mixed with an n-type organicsemiconductor, or the charge-transfer complex thin film, or the dopedconductive high molecular thin film, or a p-type organic semiconductordoped with the acceptor, or an n-type organic semiconductor doped withthe donor. In such a case, it is effective to use the charge-transfercomplex thin film in place of the inorganic thin film.

Further, by layering the n-type organic semiconductor thin film that isdoped with the donor and the p-type organic semiconductor thin film thatis doped with the acceptor to have these serve as the semiconductor thinfilm layer, it becomes a functional organic semiconductor layer intowhich the holes and the electrons can both be injected effectively.Furthermore, a technique is also considered in which the donor dopedn-type organic semiconductor thin film and the acceptor doped p-typeorganic semiconductor thin film or laminated onto one side or both sidesof the thin film in which the p-type organic semiconductor thin film andthe n-type organic semiconductor thin film are mixed together.

Note that, all the types of the thin film which are given above asstructures for the above-mentioned semiconductor thin film layer do notneed to be formed in film shapes, but rather they may be also formed asisland shapes.

By applying the above-mentioned semiconductor thin film layer in thepresent invention, it becomes possible to manufacture the organicsemiconductor element with high reliability and good yield.

As an example, the organic thin film layer of the present invention canbe structured such that light emission is obtained by flowing theelectric current, to thereby obtain the organic EL element. Thus, theorganic EL element of the present invention is also effective becausethe efficiency can also be improved.

When used in this way, the structure of the organic thin film layer(i.e., the organic EL layer) may be the organic EL element organic ELlayer structure and constitute materials that are generally used.Specifically, many variations are possible such as a laminated structuredescribed in Reference 2 with the hole transporting layer and theelectron transporting layer, and a single-layer structure using thehigh-molecular compound, and the high efficiency element using lightemission from the triplet excited state. Further, as described above,the colors from each of the organic EL layers as different emissioncolors can be mixed as different colors to enable an application as along-life white color light emission element.

Regarding the anode the organic EL element, if the light is to be madeto exit form the anode side, then ITO (indium tin oxide), IZO (indiumzinc oxide), and other such transparent conductive inorganic compoundscan be often used. An ultra thin film of gold or the like is alsopossible. If the anode does not have to be transparent (i.e., in thecase where the light is made to exit from the cathode side), then ametal/alloy and or a conductive body which does not transmit light butwhich has a somewhat large work function may be used, such as W, Ti, andTiN.

For the organic EL element cathode, a metal or alloy with a small normalwork function such as an alkali metal, alkali earth metal or rare earthmetal is used. An alloy including these metallic elements may be used aswell. For example, an Mg:Ag alloy, an Al:Li alloy, Ba, Ca, Yb, Er, andthe like can be used. Further, in the case where the light is to be madeto exit from the cathode side, an ultra thin film made of themetal/alloy may be used.

Further, for example, by using the organic thin film layer according tothe present invention as the structure that generates the electromotiveforce by absorbing the light, the organic solar battery can be obtained.Thus, the organic solar battery of the present invention is effectivebecause it improves efficiency.

When structured in this manner, the structure of the functional organicthin film layer may use the structure and structure materials that aregenerally used in the functional organic thin film layer of the organicsolar battery. A specific example is the laminated structure with thep-type organic semiconductor and the n-type organic semiconductor, suchas is described in Reference 3.

EMBODIMENTS Embodiment 1

In accordance with the present embodiment, a specific example will begiven of the organic EL element according to the present invention usingthe charge-transfer complex as the conductive thin film layer. FIG. 8shows an element structure of the organic EL element.

First, on a glass substrate 801 on which ITO as an anode 802 isdeposited into a film with a thickness of about 100 nm,N—N′-bis(3-methylphenyl)-N,N′-diphenyl-benzidine (abbreviated to TPD) asthe hole transporting material is deposited by 50 nm to obtain a holetransporting layer 804 a. Next, tris(8-quinolinolato)aluminum(abbreviated to Alq) as a light emitting material having an electrontransporting property is deposited by 50 nm to obtain anelectron-transporting and light emitting layer 805 a.

A first organic EL layer 810 a is formed in the above manner.Thereafter, TTF and TCNQ are codeposited at a ratio of 1:1 as aconductive thin film layer 806, forming a layer with a thickness of 10nm.

After that, 50 nm of TPD is deposited as a hole transporting layer 804b, and deposited on top of this is 50 nm of Alq, which serves as anelectron transporting layer/light emitting layer 805 b. Thus, a secondorganic EL layer 810 b is formed.

Finally, as the cathode 803, Mg and Ag are codeposited at an atomicratio of 10:1, and the cathode 803 is formed to have a thickness of 150nm, to thereby obtain the organic EL element of the present invention.

Embodiment 2

In accordance with this embodiment, a specific example is shown of anorganic EL element of the present invention, in which an organicsemiconductor that is the same as used in the organic EL layer isincluded in the conductive thin film layer, and the acceptor and thedonor are doped to make the organic EL element conductive. FIG. 9 showsan example of an element structure of the organic EL element.

First, 50 nm of TPD for serving as the hole transport material isdeposited onto a glass substrate 901 which has approximately 100 nm ofITO serving as an anode 902. Next, 50 nm of Alq which serves as theelectron transporting light-emission material is deposited, and thisserves as an electron transporting layer/light emitting layer 905 a.

After a first organic EL layer 910 a is formed in this way, 5 nm of alayer 906 is codeposited with the Alq so that the donor TTF constitutes2 mol %. Then, 5 nm of a layer 907 is codeposited with the TPD so thatthe acceptor TCNQ constitutes 2 mol %, to serve as a conductive thinfilm layer 911.

After that, 50 nm of TPD is deposited as a hole transporting layer 904b, and deposited on top of this is 50 nm of Alq, which serves as anelectron transporting layer/light emitting layer 905 b. Thus, a secondorganic EL layer 910 b is formed.

Finally, as the cathode 903, Mg and Ag are codeposited at an atomicratio of 10:1, and the cathode 903 is formed to have a thickness of 150nm, to thereby obtain the organic EL element of the present invention.The element can be manufactured simply by the organic semiconductor inthe organic EL layer as the material for structuring the conductive thinfilm layer, and mixing the donor and acceptor, thus being extremelysimple and effective.

Embodiment 3

In accordance with the present embodiment, a specific example is shownof a wet-type organic EL element, in which an electrical light emittingpolymer is used for the organic EL layer and the conductive thin filmlayer is formed of a conductive polymer. FIG. 10 shows an elementstructure of the organic EL element.

First, onto a glass substrate 1001 on which ITO as an anode 1002 isdeposited into a film with a thickness of about 100 nm, a mixed aqueoussolution of polyethylene dioxythiophene/polystyrene sulfonic acid(abbreviated to PEDOT/PSS) is applied by spin coating to evaporatemoisture, so that a hole injecting layer 1004 is formed with a thicknessof 30 nm. Next,poly(2-methoxy-5-(2′-ethyl-hexoxy)-1,4-phenylenevinylene) (abbreviatedto MEH-PPV) is deposited into a film with a thickness of 100 nm by spincoating to obtain a light emitting layer 1005 a.

A first organic EL layer 1010 a is formed in the above manner.Thereafter, a 30 nm film of PEDOT/PSS is applied by spin coating, toserve as a conductive thin film layer 1006.

Then, after that, a 100 nm film of MEH-PPV is applied by spin coating,to serve as a light emitting layer 1005 b. Note that, since theconductive thin film layer is made of the same material as the holeinjecting layer, this second organic EL layer 1010 b does not need ahole injecting layer formed to it. Therefore, in a case where a thirdand a fourth organic EL layer are to be laminated onto this, aconductive thin film layer PEDOT/PSS and a light-emission layer MEH-PPVcan be layered alternately according to extremely simple manipulations.

Finally, 150 nm of Ca is deposited as the cathode. On top of this, 150nm of Al is deposited as a cap to prevent oxidization of Ca.

Embodiment 4

In accordance with the present invention, a specific example is shown ofa organic solar battery of the present invention, in which a mix of thep-type organic semiconductor and the n-type organic semiconductor isapplied as the conductive thin film layer.

First, 30 nm of CuPc, which is the p-type organic semiconductor, isdeposited onto the glass substrate that has approximately 100 nm of ITOapplied onto it as a transparent electrode. Next, 50 nm of PV, whichserves as the n-type organic semiconductor, is deposited, and CuPc andPV are used to form a p-n junction in the organic semiconductor. Thisbecomes a first functional organic thin film layer.

After that, CuPc and PV are codeposited at a 1:1 ratio as the conductivethin film layer to have a thickness of 10 nm. Further, 30 nm of CuPc isdeposited, and on top of that 50 nm of PV is deposited, whereby creatinga second functional organic thin film layer.

Finally, 150 nm of Au is applied as the electrode. The organic solarbattery structured as described above is extremely effective because itcan realize the present invention simply by ultimately using only twotypes of organic compounds.

By reducing the present invention to practice, it becomes possible toprovide the organic semiconductor element which is highly reliable andhas good yield, without having to use the conventional ultra thin film.Further, particularly in the photoelectronic device using the organicsemiconductor, the efficiency of the photoelectronic device can beimproved.

1-48. (canceled)
 49. A light-emitting device comprising: an anode; afirst electroluminescent layer over the anode; a layer over the firstelectroluminescent layer, the layer comprising at least one ofmolybdenum oxide, vanadium oxide, niobium oxide, and lithium oxide; asecond electroluminescent layer over the layer; and a cathode over thesecond electroluminescent layer, wherein each of the firstelectroluminescent layer and the second electroluminescent layercomprises a hole transporting layer and an electron transporting layerover the hole transporting layer.
 50. The light-emitting deviceaccording to claim 49, wherein the layer comprises molybdenum oxide. 51.The light-emitting device according to claim 49, wherein the layercomprises vanadium oxide.
 52. The light-emitting device according toclaim 49, wherein the layer comprises lithium oxide.
 53. Thelight-emitting device according to claim 49, wherein the layer comprisesone of molybdenum oxide and vanadium oxide and lithium oxide.
 54. Thelight-emitting device according to claim 49, wherein the light-emittingdevice is capable of emitting white light.
 55. The light-emitting deviceaccording to claim 49, wherein the first electroluminescent layer andthe second electroluminescent layer emit light with different color sothat the light-emitting device is capable of emitting white light. 56.The light-emitting device according to claim 49, wherein at least one ofthe first electroluminescent layer and the second electroluminescentlayer emits light from a triplet excited state.
 57. A light-emittingdevice comprising: an anode; a first electroluminescent layer over theanode; a first layer over the first electroluminescent layer, the firstlayer comprising an electron transporting material and a donor to theelectron transporting material; a second layer over the first layer, thesecond layer comprising at least one of molybdenum oxide, vanadiumoxide, and niobium oxide; a second electroluminescent layer over thesecond layer; and a cathode over the second electroluminescent layer,wherein each of the first electroluminescent layer and the secondelectroluminescent layer comprises a hole transporting layer and anelectron transporting layer over the hole transporting layer.
 58. Thelight-emitting device according to claim 57, wherein the second layercomprises molybdenum oxide.
 59. The light-emitting device according toclaim 57, wherein the second layer comprises vanadium oxide.
 60. Thelight-emitting device according to claim 57, wherein the donor isselected from an alkali metal and an alkali earth metal.
 61. Thelight-emitting device according to claim 57, wherein the donor isselected from a Lewis base.
 62. The light-emitting device according toclaim 57, wherein the second layer is a metal oxide layer composed ofone of molybdenum oxide, vanadium oxide, and niobium oxide.
 63. Thelight-emitting device according to claim 57, wherein the second layer isa metal oxide layer composed of molybdenum oxide.
 64. The light-emittingdevice according to claim 57, wherein the light-emitting device iscapable of emitting white light.
 65. The light-emitting device accordingto claim 57, wherein the first electroluminescent layer and the secondelectroluminescent layer emit light with different color so that thelight-emitting device is capable of emitting white light.
 66. Thelight-emitting device according to claim 57, wherein at least one of thefirst electroluminescent layer and the second electroluminescent layeremits light from a triplet excited state.
 67. A light-emitting devicecomprising: an anode; a first electroluminescent layer over the anode; afirst layer over the first electroluminescent layer, the first layercomprising lithium oxide; a second layer over the first layer, thesecond layer comprising a hole transporting material and an acceptor tothe hole transporting material; a second electroluminescent layer overthe second layer; and a cathode over the second electroluminescentlayer, wherein each of the first electroluminescent layer and the secondelectroluminescent layer comprises a hole transporting layer and anelectron transporting layer over the hole transporting layer.
 68. Thelight-emitting device according to claim 67, wherein the acceptor is aLewis acid.
 69. The light-emitting device according to claim 67, whereinthe light-emitting device is capable of emitting white light.
 70. Thelight-emitting device according to claim 67, wherein the firstelectroluminescent layer and the second electroluminescent layer emitlight with different color so that the light-emitting device is capableof emitting white light.
 71. The light-emitting device according toclaim 67, wherein at least one of the first electroluminescent layer andthe second electroluminescent layer emits light from a triplet excitedstate.
 72. A light-emitting device comprising: a first electrode; afirst electroluminescent layer over the first electrode; a layer overthe first electroluminescent layer, the layer comprising at least one ofmolybdenum oxide, vanadium oxide, niobium oxide, and lithium oxide; asecond electroluminescent layer over the layer; and a second electrodeover the second electroluminescent layer, the second electrode beingtransparent, wherein each of the first electroluminescent layer and thesecond electroluminescent layer comprises a hole transporting layer andan electron transporting layer over the hole transporting layer.
 73. Thelight-emitting device according to claim 72, wherein the layer comprisesmolybdenum oxide.
 74. The light-emitting device according to claim 72,wherein the layer comprises vanadium oxide.
 75. The light-emittingdevice according to claim 72, wherein the layer comprises lithium oxide.76. The light-emitting device according to claim 72, wherein the layercomprises one of molybdenum oxide and vanadium oxide and lithium oxide.77. The light-emitting device according to claim 72, wherein thelight-emitting device is capable of emitting white light.
 78. Thelight-emitting device according to claim 72, wherein the firstelectroluminescent layer and the second electroluminescent layer emitlight with different color so that the light-emitting device is capableof emitting white light.
 79. The light-emitting device according toclaim 72, wherein at least one of the first electroluminescent layer andthe second electroluminescent layer emits light from a triplet excitedstate.
 80. The light-emitting device according to claim 72, wherein thesecond electrode comprises a metal layer.
 81. The light-emitting deviceaccording to claim 72, wherein the second electrode comprises a metallayer which contains at least one of Mg, Ag, Li, Ba, Ca, Yb, and Er. 82.A light-emitting device comprising: a first electrode; a firstelectroluminescent layer over the first electrode; a first layer overthe first electroluminescent layer, the first layer comprising anelectron transporting material and a donor to the electron transportingmaterial; a second layer over the first layer, the second layercomprising at least one of molybdenum oxide, vanadium oxide, and niobiumoxide; a second electroluminescent layer over the second layer; and asecond electrode over the second electroluminescent layer, the secondelectrode being transparent, wherein each of the firstelectroluminescent layer and the second electroluminescent layercomprises a hole transporting layer and an electron transporting layerover the hole transporting layer.
 83. The light-emitting deviceaccording to claim 82, wherein the second layer comprises molybdenumoxide.
 84. The light-emitting device according to claim 82, wherein thesecond layer comprises vanadium oxide.
 85. The light-emitting deviceaccording to claim 82, wherein the donor is selected from an alkalimetal and an alkali earth metal.
 86. The light-emitting device accordingto claim 82, wherein the donor is selected from a Lewis base.
 87. Thelight-emitting device according to claim 82, wherein the second layer isa metal oxide layer composed of one of molybdenum oxide, vanadium oxide,and niobium oxide.
 88. The light-emitting device according to claim 82,wherein the second layer is a metal oxide layer composed of molybdenumoxide.
 89. The light-emitting device according to claim 82, wherein thelight-emitting device is capable of emitting white light.
 90. Thelight-emitting device according to claim 82, wherein the firstelectroluminescent layer and the second electroluminescent layer emitlight with different color so that the light-emitting device is capableof emitting white light.
 91. The light-emitting device according toclaim 82, wherein at least one of the first electroluminescent layer andthe second electroluminescent layer emits light from a triplet excitedstate.
 92. The light-emitting device according to claim 82, wherein thesecond electrode comprises a metal layer.
 93. The light-emitting deviceaccording to claim 82, wherein the second electrode comprises a metallayer which contains at least one of Mg, Ag, Li, Ba, Ca, Yb, and Er. 94.A light-emitting device comprising: a first electrode; a firstelectroluminescent layer over the first electrode; a first layer overthe first electroluminescent layer, the first layer comprising lithiumoxide; a second layer over the first layer, the second layer comprisinga hole transporting material and an acceptor to the hole transportingmaterial; a second electroluminescent layer over the second layer; and asecond electrode over the second electroluminescent layer, the secondelectrode being transparent, wherein each of the firstelectroluminescent layer and the second electroluminescent layercomprises a hole transporting layer and an electron transporting layerover the hole transporting layer.
 95. The light-emitting deviceaccording to claim 94, wherein the acceptor is a Lewis acid.
 96. Thelight-emitting device according to claim 94, wherein the light-emittingdevice is capable of emitting white light.
 97. The light-emitting deviceaccording to claim 94, wherein the first electroluminescent layer andthe second electroluminescent layer emit light with different color sothat the light-emitting device is capable of emitting white light. 98.The light-emitting device according to claim 94, wherein at least one ofthe first electroluminescent layer and the second electroluminescentlayer emits light from a triplet excited state.
 99. The light-emittingdevice according to claim 94, wherein the second electrode comprises ametal layer.
 100. The light-emitting device according to claim 94,wherein the second electrode comprises a metal layer which contains atleast one of Mg, Ag, Li, Ba, Ca, Yb, and Er.